Wednesday, November 27, 2013

Converting a Mail User to a Remote User Mailbox

I have an client with an existing Office 365 implementation and a separate on-premises Exchange organization. As part of linking these two together into hybrid mode, the local AD account became a Mail User.

A Mail User is a local AD account with an external SMTP address configured. This allows the user to have an email address in the GAL, but is not a local Exchange mailbox.

To move mailboxes, this Mail User needs to be configured as a Remote User Mailbox. A Remote User Mailbox also has a proper remote routing address property configured.

I couldn't find any documentation on performing this process. However, I did find a script that indicates it fixes up user accounts when a mailbox move to Office 365 does not complete properly. I used this script to identify the changes that needed to be made.

Configure the user attribute targetaddress to contain the remote routing address for the mailbox. This should be in the format of userid@domain.mail.onmicrosoft.com. In my case it would have been testmailbox@byronwright.mail.onmicrosoft.com.

Set the msExchRemoteRecipientType attribute for the user account to equal 4.

Set the msExchRecipientDisplayType attribute for the user account to equal -2147483642. (yes, this is a negative value)

Set the msExchRecipientTypeDetails attribute for the user account to equal 2147483648.

Those steps changed the Mail User to a Remote User Mailbox. However, I was still unable to move the mailbox from Office 365 to the on-premises Exchange. This was due to the ExchangeGUID attribute not being set properly on the local user account. To fix this, I performed the following:

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About Me

A consultant, author, and instructor for about 20 years. My areas of expertise are Windows Server, Exchange Server, and Office 365. While my primary role is a consultant, I also provide technical training (custom and Microsoft authorized). I have been part of a team authoring Microsoft Official Curriculum on Windows Server, Active Directory, and Exchange Server since 2003. I have also authored books for Microsoft Press, Cengage Learning, and Wiley. I was also a Microsoft MVP for Exchange Server/Office 365 (2012-2015).@ByronWrightGeekwww.btwsolutions.ca